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10th EEGS Symposium on the Application of Geophysics to Engineering and Environmental Problems
- Conference date: 23 Mar 1997 - 26 Mar 1997
- Location: Reno, Nevada, USA
- Published: 23 March 1997
101 - 106 of 106 results
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The Search For Ancient Helike: A Gpr Case Study
Authors Doria L. Kutrubes, Steven Soter and Dora KatsonopoulouIn 373 BC, the Classical city of Helike, on the Gulf of Corinth in Greece, was destroyed by a catastrophic
earthquake and mass-movement of the deltaic sediments upon which it was built. Due to subsequent burial by
sedimentation, and tectonic uplift of the northern Peloponnesos, the ruined site is now believed to be on land. Since 1988,
the search for Helike has been conducted using sonar, bore hole drilling, geophysical survey (including magnetometry and
GPR), and excavation.
In June 1996 we used GPR in seven areas near the presumed site of Helike. Data collected using GSSI’s SIR-2
and monostatic 400 MHz antemra achieved a maximum penetration of 3 m using filters and a running weighted average
stack. Despite limited resolution and penetration, we observed several hyperbolic targets. One of these was a tile floor
dating from the Roman Era. GSSI’s multi-low-frequency bistatic antenna, used in the 80 MHz configuration, achieved
depths of approximately 5 to 6 meters in some areas.
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Rapid-Response Geophysical Site Investigations At A Pre-Columbian Settlement In Honduras
More LessElectrical resistivity and a non-traditional seismic investigation technique were applied in
support of an archaeological investigation of a Pre-Columbian settlement in eastern Honduras. Field
studies were scheduled to be completed within a three-week window, so rapid response was critical to
the project. Electrical resistivity measurements were conducted in the profiling mode, using Wenner and
Lee configurations, at electrode spacings of 2 and 4 m. Seismic measurements were performed using the
SASW method, which is a surface-based technique using Rayleigh-type surface waves. Numerous
shallow anomalies were identified. Excavations revealed stone pavements, a carved stone, and a
human burial. Deeper anomalies prompted excavations which revealed a thick area1 fill above the
archaeologically sterile alluvium.
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Non-Destructive Evaluation And Three Dimensional Visualization Of An Ancient Egyptian Artifact With Applications To Modern Engineering Materials
Authors D. Wiese, D.W. Holdsworth and M.D.A. ThomasTraditionally, the study of ancient cultures is concerned with the excavation of habitations, monuments
and the retrieval of artifacts, however one may also gain specific knowledge about a civilization on a
smaller scale, that of the artifact itself. By using non-destructive evaluation techniques such as industrial
computed tomography (CT) x-rays and scientific visualization, information can be obtained about the
internal composition and structure of an object at resolutions of millimeters or even microns. As this type
of data acquisition is non-destructive and non-invasive, the technique has profound implications in the
analysis of materials in the fields of archaeology as well as other areas of science and engineering. For
ancient artifacts, this may be the only means of non-destructively determining the structural integrity and
composition of rare, precious and fragile objects, thereby contributing to their authenticity and valuation.
In this paper, the results of a study of an ancient Egyptian cat mummy using a high resolution XRII based
quantitative volume CT scanner are presented. The study was initiated to confirm the internal
composition of the mummy and to discover further details about its contents and method of preservation.
This methodology produced meaningful results that enabled a more complete understanding of an artifact
that could not otherwise be achieved without disturbing the artifact. Applications related to other fields
such as civil engineering (composition and structure in concrete drillcore) are also discussed.
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Scattering Of Surface Waves At Anisotropic Wave Barriers
Authors Elizabeth Its and Jong LeeIn this paper we consider the screening effectiveness of an infilled trench for isolation from
near-surface ground-transmitted vibrations. The infilled trench is modeled by a vertical
anisotropic layer embedded into an isotropic half-space. To study surface wave scattering
at the layer we employ the Green’s function technique. The narrow anisotropic layer is
modeled by a matrix operator which relates displacement and stress fields at the left-hand
side and right-hand side of the layer. The matrix operator is obtained using Taylor’s series
decomposition. To represent the field inside the thick layer we apply forward-backward
decomposition of the field and calculate forward and backward scattering coefficients of
the layer. The results of calculations for the anisotropic layers are compared with similar
calculations for various isotropic layers.
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Geophysical Characterization Of The Upper Borrego Valley, California
More LessA horizontal and vertical array of strong motion accelerometers, located in the upper Borrego Valley, California, has
been monitoring earthquakes since 1992. One and two-dimensional modeling of elastic wave propagation have been
unsuccessful in predicting ground motion in the valley and, therefore, three-dimensional (3-D) modeling was
required. In order to simulate 3-D elastic wave propagation in the valley, it was necessary to develop a 3-D model of
density, compressional (P) and shear (S) wave velocities for the shallow basin. A geophysical investigation,
combining both surface and borehole methods, was conducted to develop this model.
Several surface geophysical techniques were used during this investigation including the time-domain
electromagnetic (TDEM), seismic refraction, and gravity methods. The surface geophysical surveys were designed
to map approximate depth to groundwater and crystalline basement - the two features which were expected to have
the most significant effects on density and velocity (P-wave velocity only at the water table). Thirty-five TDEM
soundings were conducted at selected locations in the valley to map depth to groundwater and basement. Seismic
refraction soundings were conducted at 16 locations to determine approximate depth to groundwater. Gravity
measurements were made at 627 stations in the valley to map depth to crystalline basement.
P and S-wave velocity measurements were made in two boreholes using a suspension logging system to develop a
velocity-depth model for the basin, Resistivity, spontaneous potential (SP), and natural gamma logs were also
obtained in the two boreholes. The resistivity logs were used to help constrain TDEM modeling. Density
measurements were made on soil samples collected from the unsaturated zone while drilling the boreholes to
constrain subsurface densities.
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Opportunities Of Acoustic Sounding In The Potash Mines
More LessFor several years, acoustic sounding has been used in the potash mines of the Upper
Kama potash mining district to solve mining problems. Salt rock has a relatively low
attenuation rate of elastic waves so that it allows one to use high frequency acoustic
signals for probing a salt rock deposit of a substantial thickness. A custom-made, PC
supplied acoustic acquisition system is used to record a signal envelope, generated by a
radio impulse at a 0.04 millisecond digitization rate. The operating frequencies are 10 or
20 kHz. Piezoceramic transducers are attached to the roof of the mine with specially
designed poles. The acoustic reflection data is collected mainly by using zero offset
profiling and an expanding spread mode. Background noise is a major complication in
record acquisition, and computer processing uses correlation filtering to remove the noise
patterns from the records. The acoustic reflection data obtained shows a good level of
agreement with synthetic acoustograms calculated from the stratigraphy found in nearby
boreholes with depths ranging up to 100 meters. The high frequency acoustic reflection
method has been proven to be capable of mapping the stratigraphic features of flat bedded
and folded salt rocks, and to find zones of disturbed rock around the mine openings.
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